It is known that metals, such as silver, gold, palladium, platinum, copper, and zinc, effectively kill microbes. Therefore, many applications of using the antimicrobial effect of such metals have been proposed. An example of such application is a wound dressing. Moreover, it has been disclosed that a noble metal such as silver and an activated carbon are used together in the water treatment of wastewater and drinking water. For recycling use, silver is preferably carried on the activated carbon. The activated carbon can remove the impurities in water, while the silver can kill the microbes on the activated carbon. Contamination resulting from the growth of microbes due to the bioaffinity of the activated carbon is thereby, prevented.
The usage form of the activated carbon comprises activated carbon fiber, activated carbon granule, and activated carbon powder. Recently developed in the 70's, the activated carbon fiber is an adsorption material with superior performance. Compared to the conventional granulated or powdered activated carbon, the activated carbon fiber similarly has a large number of open pores, superior adsorption property, good antibiotic resistance, hydrophilic property, electron supply ability, and high specific surface area. However, the activated carbon fiber has a different molecular structure, appearance, and structures of pores on the surface. Specifically, the activated carbon fiber allows for more diffusion during adsorption and desorption and can be fabricated into various forms, such as felt or cloth, in a second process. Moreover, the activated carbon fiber has a greater specific surface area and adsorption efficiency and is readily utilized.
Ling Wang, Shurong Li and Fenggang An disclosed in CN1103054 (1995) that the market selling pure charcoal was washed with distilled water. After drying and cooling, it was co-impregnated with a prepared solution of AgNO3 and NH3H2O and vibrated. After removing the water phase, re-drying and cooling, it was co-impregnated with a prepared solution of KI and vibrated, and then a silver-containing activated carbon was obtained after drying, washing and re-drying. The silver-containing activated carbon could then be used as a filtering material in the mineral spring pot to inhibit the bacterial growth in the pot so as to increase the quality of drinking water.
Suzuki Mitsuo, Hirahara Satoshi, and Okurama Kohei disclosed in JP10099678 (1998) that a silver compound was added to a raw material of activated carbon, i.e., coal, before manufacturing the activated carbon. The mixture was then subjected to heat treatment and an activation process to obtain a silver-containing activated carbon.
Okura Yukio disclosed in JP57019083 (1982) that the activated carbon was first immersed in a silver compound, e.g., silver salt. Then, steam was injected into the immersed activated carbon for a heat treatment at a temperature slightly lower than the melting point of the silver salt to produce a silver-containing activated carbon.
To form silver on activated carbon fibers for the antibacterial effect, A. Oya, T. Wakahara, and S. Yoshida mentioned in Carbon, 31, 1243-1247, 1993 that a silver acetate solution was mixed with pitch, and then spun and stabilized. Afterwards, the activation process was conducted using steam at a temperature of 900° C. to manufacture activated carbon fiber containing up to 0.03 wt % of silver. Nonetheless, Oya et al. consider that this method still had problems which included improving the spinning process, controlling activation conditions and finding a way to produce silver-containing activated carbon fibers with a high specific surface area.
C. Y. Li, Y. Z. Wan, J. Wang, Y. L. Wang, X. Q. Jiang, and L. M. Han mentioned in Carbon, 36, 61-65, 1998 that pitch-based activated carbon fiber was impregnated in an unsaturated silver nitrate solution for 12 hours and then thermally cracked in nitrogen gas at a temperature of 420° C. for 30 minutes to obtain a silver-containing pitch-based activated carbon fiber. However, Li et al. considered that this method still was unable to evenly distribute the silver particles and prevent the precipitation of silver in water.
The inventors of the subject application repeated the method provided by Li et al. and also found the above drawbacks. The impregnation process used by Li et al. was the same as that disclosed in CN1103054 and JP5701908 and the results were identical. All of the problems, such as the size and distribution of silver particles and their precipitation in water, could not be resolved.
Furthermore, as known by persons skilled in the art, the noble metals often have a catalytic function, in addition to an antibacterial benefit. For example, it has been known that silver can be used in the following catalytic applications: the catalytic oxidation of olefins for preparing olefin oxides, the selective catalytic hydrogenation of acetylene in an ethylene stream for purifying the ethylene stream, and the catalytic oxidation of carbon monoxide in cigarette smoke for converting it to carbon dioxide. The aforementioned catalytic applications can be found in US2006/0178262A1, US2006/0205963A1, and US2005/0279372A1, which are incorporated hereinto for reference.
Given the above concerns, it is now important to find a proper process for effectively carrying a metal, such as silver, on a substrate much like a carbonaceous material with a high specific surface area to enhance its applicability.
The subject invention improves on the method for manufacturing a metal-carrying carbonaceous material. In particular, the method provides a carbonaceous material with a low metal leachability in water, especially a carbonaceous material which conforms to the drinking water standard of the United States, i.e., having a silver leachability of lower than 50 ppb.